High temperature quench method



May 30, 1967 M. M. YURKo ETAL HIGH TEMPERATURE QUENCH METHOD Filed Feb.1, 1963 United States Patent O 3,322,412 HIGH TEMPERATURE QUENCH METHODMalvin M. Yurko, Whippany, NJ., Vernon 0. Bowles, Bedford, and AlphonseA. Corona, Jr., Hempstead, N.Y., and Walter F. Read, Westfield, NJ.,assgnors to Mobil Oil Corporation, a corporation of New York Filed Feb.1, 1963, Ser. No. 255,569 5 Claims. (Cl. 261-128) The present inventionrelates to an improved method for quenching the gaseous eiiiuents ofhigh temperature reactions. It is more particularly concerned withcooling the hot etiiuent products of vapor phase reactions ofhydrocarbons and, more specically, with quenching the effluent from thehigh temperature thermal hydrodealkylation of alkyl aromatichydrocarbons.

Various devices have been proposed for quenching hot reaction products,usually in vessels separated from the reaction vessels. Although thequenching of reaction products within the actual reaction vessel isknown, trouble has sometimes been encountered with the undesirablecooling of the reactants which are still reacting and often diii'icultyis experienced from the deposition of carbon at an excessive rate.Accordingly, there is a demand for quenching systems which are free fromthese diiculties.

Quenching within the reactor is important in the case of the thermalhydrodealkylation of alkyl aromatic compounds as the high temperaturereaction eiiiuents contain substantial'quantities of hydrogen and lowerhydrocarbons, such as methane. Such eiiiuents can rapidly cause metaldusting at temperatures above about 12757 F. at pressures of the orderof 500 pounds per square inch. Metal dusting is a form of catastrophiccorrosion that is believed to involve carburization of steels, includingmany types of stainless steel, and this attack is often so fast that itis impractical to even attempt to calculate a corrosion allowance. Also,the strength of metals, including heat-resistant stainless steel alloys,is greatly reduced at high temperature levels, and it is customary tocompensate for this by using equipment with thicker walls at a highercost. However, equipment with heavier walls introduces additionalproblems by reason of-the greater stresses set up in thermal expansionand contraction. The present invention is particularly intended toalleviate these diculties by rapid cooling of such eiiiuents before theyleave the reactor.

An object of the invention is to provide an improved method of quenchinghigh temperature gaseous materials.

Still another object of the invention is to minimize or prevent metaldusting by the etliuent from a high temperature reaction.

A still further object of the invention is to substantially reduce theweightand cost of the heat resistant equipment utilized downstream of areactor for handling the products of a high temperature reaction.

Yet another object of the invention is to substantially reduce thestresses and strains created in equipment handling the effluent of ahigh temperature reaction.

Other objects and advantages of the invention will be apparent to thoseskilled in the art upon consideration of the detailed disclosure whichfollows.

This invention is concerned with a process which comprises quenching thehot effluent of a gaseous phase reaction at high temperature within theconfines of an enclosed reaction vessel by passing said effluentupwardly in a confined space within said vessel through a permeablemember flooded with a vaporizable quench liquid at a sutiiciently highgas flow rate with respect to the number and size of the openings insaid permeable member to retain at least a major portion (preferablysubstantially all) of the vaporizing quench liquid above said permeablemember. In one embodiment of the invention, the quenched eiiiuent issubjected to vortical flow during withdrawal through an outlet passageto vaporize any entrained droplets of quench liquid by impingementagainst a hot wall of said passage.

For a better understanding of the nature and objects of this invention,reference should be had to the accompanying drawing in which the ligureis a fragmentary sectional view taken along the longitudinal axis of thelower part of a reactor and showing a preferred embodiment of aquenching device. For greater clarity, a number of minor constructiondetails have been omitted, particularly fastenings, such as bolts orstuds, rivets, etc.

The drawing shows the lower part of a thermal hydrodealkylation reactorfor the production of benzene from an alkyl benzene, such as toluene,and hydrogen. This reactor may also be employed for the production ofnaphthalene from various alkyl naphthalenes. In the production of bothbenzene and naphthalene, the ternperature of the etiiuent reactionproducts is typically of the order of 1200 to 1400 F. and after passingthrough the quenching device described hereinafter, the temperature ofthose reaction products is reduced about Z50-400 to a temperature levelwhere metal dusting and/or the reduction in metal tensile strength areno longer problems.

The drawings shows the bottom of a reactor having a heavy shell 2 ofrelatively low alloy steel inasmuch as the layer of refractoryinsulation 4 protects the shell from direct exposure to the hot gaseousreaction mixture. However, the structural elements of the quench deviceare not similarly protected; and it is recommended that these beconstructed of an austenitic stainless steel, such as type 304, one ofthe 18% chromium and 8% nickel alloys.

The quench assembly consists of an enclosure made up of cylindricalhousing 6 attached to a base plate 8 which prevents liquid fromcontacting the refractory insulating cement in order to avoid thedeterioration of this refractory material. The cover 10 is riveted tothe flange 12 which is fastened to housing 6. This joint, like the otherjoints in the quench device, is not subjected to any significantpressure differential and therefore need not be made pressure tight.

Arched openings 14 are regularly spaced around the circumference of thewall 6 at its lower end to admit downwardly owing reaction products ineven distribution into the enclosure and allow them to rise through thefoam and sprays of quenching liquid described hereinafter. The spaceenclosed by the housing 6 and top 10 is divided into a lower chamber 16and an upper chamber 18, usually of greater height than chamber 16, by apermeable member, such as perforate plate 20, which is attached byrivets to welded flange 22 on wall 6 and to welded iiange 24 on the8-inch outlet pipe 26. For a gas flow in the range of 800,000 to1,500,000 standard cubic feet per hour, plate 20 is drilled with 284holes 28 of 1 diameter spaced evenly in the form of a grid with thecenter lines approximately 2.5 apart.

A quench liquid is pumped into the extremely hot gaseous product of thereator in the upper chamber 18 as the product is on its way out ofthereactor. The quench liquid enters a supply pipe (not shown) whichbranches into a curved or Y-branch manifold 30 having two armsvextending on opposite sides of the outlet line 26 and termminating inthe nozzles 32 which are disposed 180 apart relative to the circularplate 20. These nozzles, which are merely unrestricted orifices at theends of the pipes in this illustration, are directed downwardly, sinceit is desired that the cooling action of the vaporizing liquid beprimarily utilized to cool the gases which have already left the activereaction space in the reactor. In the case of an endothermic reaction,it is desirable to avoid contact of the cooling liquid with quenchchamber top so far as may be practicable, for such contact would coolthe top and allow it to absorb heat from the reacting gases in thereaction space thereabove. This cooling of the reactants would not onlyrequire a greater degree of heating or preheating of the charge butwould slow down the reaction rate and increase the cost of pumpingsufficient liquid for the quenching operation.

To break up the jets of quench liquid and distribute them over thesurface of the perforate plate 20, a circular distributing or splashplate 34 is suspended below each nozzle 32 about half of the distancedownward towards plate 20. Each splash plate hangs from three straps 36which are welde-d to the side of the pipe nozzle 32 and to plate 34.These straps 36 are radially disposed at 120 intervals around thenozzles and splash plates with the intervening spaces open to permit theliquid to be freely distributed over the surface of perforate plate 20.

The Y-branch manifold 30 is supported on a U-shaped bracket 38 whichextends around half of the pipe 26 to which it is secured by welding orbolts and the open end of the U projects out under the manifold.

The quench liquid employed in this invention is desirably a product ofthe present process in either crude or purified state, for examplebenzene; this eliminates contamination and the necessity forfractionating the quenched effluent. For example, in the thermalhydrodealkylation of toluene into benzene, it is preferred to usecondensed reactor eflluent as the quench liquid. However, other highboiling liquids inert to the gaseous material -being quenched can beused for the purpose, if so desired.

There are a number of optional but highly desirable features of thenovel device. Among these is the dam or shield 40 open at the top 42 andsurrounding the lower chamber 16 and the lower part of the upper chamber18 approximately to the level of the nozzles 32. This dam serves toprevent the passage of any quench liquid which reaches the floor 8 ofthe lower chamber from emerging into the main reaction space of thereactor and from contact with the surrounding insulation.

Another optional but generally desirable feature is the swirl bailleassembly 44 located in the outlet conduit 26 to induce a swirling orvortical motion in the exit stream of quenched material passing downwardin the line 26 sufficient to direct any entrained droplets of liquid ofsubstantial size onto the walls of the conduit where they are quicklyvaporized by the relatively hot surface of the pipe 26. This baille ismade up of three semi-elliptical sections 46 of stainless steel platewelded to a short length of l-inch pipe 48 at an angle of 50 with thelongitudinal axis of pipe 26. The three baille sections are spacedequidistantly or 120 apart around the tube 48, and the entire assemblyis fastened in place by welding it to the pipe 26.

Other types of swirl baflles may also be employed including a twistedstrip of sheet metal. In fact, any design may be used that imparts acentrifugal component to the motion of the quenched eflluent productspassing therethrough. This baflle is desirably located well within thepressure bearing shell 2 of the reactor in order that any froth or drops`of entrained liquid will impinge on a wall section outlet conduit thatis also located within the reactor shell and therefore not subject to asubstantial pressure differential. It is preferable to avoid the suddenand perhaps random chilling of a pipe wall under heavy pressure causedby rapid vaporization of a relatively cool liquid.

In operating one modification of the present invention, the gaseousproducts of a thermal dealkylation reaction taking place at an averagereaction temperature of 1260 F. in converting toluene by reaction withhydrogen in excess into benzene and methane reach the bottom of thereactor. This effluent passes over the upper end 42 of the shield 40 andthen enters the lower chamber 16 through the openings 14. Next, thegaseous products rise vertically through the hole 28 in the perforateplate 20 and enter the upper chamber 18. Crude benzene product isdischarged from nozzles 32 as the quench liquid and produces in chamber18 a spray or foam in which the rising gases are cooled by evaporationof the liquid. The discharge rate -of the benzene product is 1.5 lbs.per lb. of toluene feed charged. After passing through the upper cell,the quenched effluent enters the line 26 and passes around swirl baflleassembly 44 where any entrained liquids is thrown by centrifugal forceonto the interior surface of pipe 26 to vaporize. The temperature of thecooled effluent leaving baffle 44 is 950 F.

In a preferred embodiment, no substantial quantity of quenching liquidis allowed to reach the lower chamber; and the principal quenchingaction occurs in the sprays splashing ofl of the plates 34 in alldirections as well as in the resulting mixed phase foam of gaseousproducts bubbling through the vaporizing liquid of which at least amajor portion is located above the perforate plate 20. The retention ofthe liquid and mixed phases essentially as foam in upper chamber 18, isaccomplished by selecting the number and diameter of the holes 28relative to the rate of gaseous flow through plate 20 to create a gasvelocity through the holes 28 of at least about 10 feet per second whileproviding suflicient openings for intimate contact between the liquidand gaseous phases and to avoid an excessive pressure drop across theplate. In general, relatively large openings are provided throughout thedevice to minimize difliculties from possible carbon formation. For thatreason, nozzles with large single orifices discharging onto horizontaldistributing plates are preferred to nozzles with a plurality of smallerorifices discharging horizontal jets of liquid.

It will be apparent to those skilled in the art that the invention maybe utilized in many forms other than that illustrated in the drawingespecially with apparatus of different configuration to provide othersuitable sprays, passages and chambers of various shapes which willaccomplish the sarne purpose. For instance, the device could easily beinstalled at the top instead of at the bottom of a reactor byrearranging outlet pipe 26 to lead the quenched products upward fromchamber 18 and by sealing the central openings in plates 8 and 20 whichwere provided for a downwardly extending pipe 26. A variety of permeablemembers may be substituted for plate 20, as for example a woven screenof thick wire or small rods, or one or more layers of parallel flatbars, channel or angle sections, alternate layers being preferablyoriented at right angles to adjacent layers. However, a flat plateperforated with holes of selected size and distribution is preferred asaffording better control in maintaining a maximum of the liquid in theupper chamber. Where there is any tendency for the gaseous material tobe significantly reheated by heat received from the cover 10 immediatelyafter that material has been quenched in the upper chamber, thisdifliculty, may be overcome by afiixing a layer of refractory insulationto the cover to greatly reduce the transmission of heat therethrough.Accordingly, the invention should not be considered as limited in anyother respects than the language of the appended claims and as may beIrequired by the prior art.

We claim:

1. In a process for the reaction of materials in the gaseous phase athigh temperatures in a confined reaction zone within an enclosedreaction vessel followed by the quenching of the resulting hot gaseouseffluent of said reaction, the improvement which comprises introducing avaporizable quenching liquid above a permeable member having openings ofpredetermined number and size into a separate confined quenching zonewithin said vessel at a rate Suicient to quench the gaseous eflluent ofsaid reaction to a substantially lower temperature upon the.

evaporation of said liquid in contact with said effluent, quenching thehot gaseous reaction eluent within said quenching zone by passing saidgaseous eflluent upwardly through said permeable member into contactwith said liquid at a suiciently high flow rate with respect to thenumber and size of the openings through said permeable member to retainat least a major portion of the Vaporizing quench liquid above saidpermeable member and withdrawing the quenched eluent from said vessel.

2. A process according to claim 1 in which the number and area ofopenings through said permeable member are suiciently restricted and theow rate of gaseous effluent upwardly through said member is suicientlyhigh to substantially eliminate the passage of quench liquid downwardthrough said permeable member.

3. A process according to claim 1 in which said gaseous effluentcomprising a dealkylated aromatic compound in admixture with methane andhydrogen is quenched from a reaction temperature exceeding 1200 F. to atemperature below about 1000 F. by the introduction at a temperaturesubstantially below 1000 F. of a quench liquid comprising a portion ofsaid `dealkylated compounds.

4. A process according to claim 1 in which said quenched elluent issubjected to vortical ow in an outlet passage from said reaction vesselhaving a wall of said passage maintained at a temperature substantiallyabove the boiling point of said quench liquid under the prevailingconditions to impinge any entrained droplets of quench liquid on thewall of said outlet passage and Vaporize said droplets during withdrawalof said quenched eHuent from said vessel.

5. A process according to claim 4 in which said vessel is maintained ata high internal pressure and vortical ow is initiated and saidvaporization -of entrained droplets occur within a section of the outletpassage located within said vessel.

References Cited UNITED STATES PATENTS 1,483,348 2/1924 Hayes et al55-257 X 1,920,623 8/1933 Becker 261-108 2,781,251 2/1957 Howell 23--2773,213,150 10/1965 Cabbage 260-672 X 3,219,419 11/1965 Braconier et al23-277 HARRY B. THORNTON, Primary Examiner. R. R. WEAVER, E. H. RENNER,Assistant Examiners.

1. IN A PROCESS FOR THE REACTION OF MATERIAL IN THE GASEOUS PHASE ATHIGH TEMPERATURES IN A CONFINED REACTION ZONE WITHIN AN ENCLOSEDREACTION VESSEL FOLLOWED BY THE QUENCHING OF THE RESULTING HOT GASEOUSEFFLUENT OF SAID REACTION, THE IMPROVEMENT WHICH COMPRISES INTRODUCING AVAPORIZABLE QUENCHING LIQUID ABOVE A PERMEABLE MEMBER HAVING OPENINGS OFPREDETERMINED NUMBER AND SIZE INTO A SEPARATE CONFINED QUENCHING ZONEWITHIN SAID VESSEL AT A RATE SUFFICIENT TO QUENCH THE GASEOUS EFFLUENTOF SAID REACTION TO A SUBSTANTIALLY LOWER TEMPERATURE UPON THEEVAPORATION OF SAID LIQUID IN CONTACT WITH SAID EFFLUENT, QUENCHING THEHOT GASEOUS REACTION EFFLUENT WITHIN SAID QUENCHING ZONE BY PASSING SAIDGASEOUS EFFLUENT UPWARDLY THROUGH SAID PERMEABLE MEMBR INTO CONTACT WITHSAID LIQUID AT A SUFFICIENTLY HIGH FLOW RATE WITH RESPECT TO THE NUMBERAND SIZE OF THE OPENINGS THROUGH SAID PERMEABLE